APPLICATIONS OF GPS IN POWER ENGINEERING

What is GPS? GPS or Global Positioning Systems is a highly sophisticated navigation system developed by the United States Department of Defense. This system utilizes satellite technology with receivers and high accuracy clocks to determine the position of an object.

The Global Positioning System A constellation of 24 high-altitude satellites A constellation of satellites, which orbit the earth twice a day, transmitting precise time and position (Latitude, Longitude and Altitude) Information.

GPS at Work Navigation - Where do I want to go? Location - Where am I? 3. Tracking - Monitoring something as it moves 4. Mapping - Where is everything else? 5. Timing - When will it happen? Properly executed, effective controls and planning will minimize the risk of undue delays in project performance. GAI’s Management Team will assist Alcoa’s staff to ensure that the project meets current professional and regulatory standards. GAI will facilitate consultation and communication among all participants, including regulatory agencies and other appropriate parties. Our management plan and assignment of key staff are designed to provide pertinent and competent technical services, efficient project scheduling, timely delivery of quality technical documents, and cost control.  

Why do we need GPS? Safe Travel Traffic Control Resource Management Defense Mapping Utility Management Property Location Construction Layout

Global Positioning Systems (GPS) Applications in Power Systems

Power companies and utilities have fundamental requirements for time and frequency to enable efficient power transmission and distribution. Repeated power blackouts have demonstrated to power companies the need for improved time synchronization throughout the power grid. Analyses of blackouts have led many companies to place GPS-based time synchronization devices in power plants and substations

GPS time synchronization By synchronizing the sampling processes for different signals – which may be hundreds of kilometers apart – it is possible to put their phasors in the same phasor diagram

GPS time synchronized pulses GPS time synchronization V V1 V2 Substation 1 Substation 2 t1 t2 t3 t4 t5 t6 t7 GPS time synchronized pulses Ψ FFT or any other technique gives: Magnitude Phase angle With respect to GPS

Absolute Time Reference Across the Power System With these recording devices, we can acquire event reports at different power system locations with simultaneously acquired samples, as the figure shows. We can use these synchronously sampled event records to analyze system-wide disturbances faster than if we tried to synchronize the event records manually.

Phasor Measurement Units PMUs Synchronized phasor measurements (SPM) have become a practical proposition. As such, their potential use in power system applications has not yet been fully realized by many of power system engineers.

Phasor Measurement Units (PMU) [or SYNCHROPHASORS]

THE GRID SYNCHRONIZATION DAWN OF THE GRID SYNCHRONIZATION

Phasor Measurement Units Phasor Measurement Units PMUs Phasor Measurement Units )PMU) They are devices which use synchronization signals from the global positioning system (GPS) satellites and provide the phasor voltages and currents measured at a given substation.

PMU input output Secondary sides of the 3Φ P.T. or C.T. Phasor Measurement Units PMUs PMU input output Corresponding Voltage or Current phasors Secondary sides of the 3Φ P.T. or C.T.

Phasor Monitoring Unit (PMU) Hardware Block Diagram:

Sampling at Fixed Time Intervals Using an Absolute Time Reference Traditionally, synchronized phasor measurement devices acquire data at fixed time intervals. These devices use an external time source with absolute time reference, such as a global positioning system (GPS) clock, to determine the sampling interval. This figure includes a hardware low-pass filter (Hardware LPF) for anti-aliasing and an analog-to-digital (A/D) converter for analog-to-digital conversion. The GPS clock controls A/D acquisition time. The main advantage of this acquisition system is that the data preserve the frequency information of the power system. For example, you can analyze power system frequency excursions during power system disturbances. This data acquisition system is also suitable for synchronized phasor measurement when an external time source with absolute time reference determines the sampling interval. 18

The GPS receiver provides the 1 pulse-per-second (pps) signal, and a time tag, which consists of the year, day, hour, minute, and second. The time could be the local time, or the UTC (Universal Time Coordinated). The l-pps signal is usually divided by a phase-locked oscillator into the required number of pulses per second for sampling of the analog signals. In most systems being used at present, this is 12 times per cycle of the fundamental frequency. The analog signals are derived from the voltage and current transformer secondary's.

Phasor Measurement Unit’s All real-time data acquisition starts here - with Phasor Measurement Unit’s – PMU’s – the heart of the matter. They don’t look like much – but despite their humble appearance, these little boxes can and do produce volumes of data (trust me ). They constantly measure key electrical states, such as phase angles and frequency, at speeds of up to 120 samples per second. TVA’s Super PDC works with data directly from these units or from their parent concentrators. The protocol’s implemented by the TVA Super PDC allow it the flexibility to work with most all PMU’s.

central data collection Phasor Measurement Units PMUs central data collection

Data Concentrator (Central Data Collection) ABB

Different applications of PMUs in power system

Applications of PMU in power System Adaptive relaying Instability prediction State estimation Improved control Fault recording Disturbance recording Transmission and generation modeling verification Wide area Protection Fault location

Applications of PMU in power System 1-Adaptive relaying Adaptive relaying is a protection philosophy which permits and seeks to make adjustments in various protection functions in order to make them more tuned to prevailing power system conditions

2-Instability prediction Applications of PMU in power System 2-Instability prediction • The instability prediction can be used to adapt load shedding and/or out of step relays. • We can actually monitor the progress of the transient in real time, thanks to the technique of synchronized phasor measurements.

Applications of PMU in power System 3-State estimation • The state estimator uses various measurements received from different substations, and, through an iterative nonlinear estimation procedure, calculates the power system state. • By maintaining a continuous stream of phasor data from the substations to the control center, a state vector that can follow the system dynamics can be constructed. • For the first time in history, synchronized phasor measurements have made possible the direct observation of system oscillations following system disturbances

Applications of PMU in power System 4-Improved control • Power system control elements use local feedback to achieve the control objective. The PMU was necessary to capture data during the staged testing and accurately display this data and provide comparisons to the system model. The shown figure shows a typical example of one of the output plots from the PMU data

Applications of PMU in power System 5-Fault Recording • They can capture and display actual 60/50 Hz wave form and magnitude data on individual channels during power system fault conditions.

6-Disturbance Recording Applications of PMU in power System 6-Disturbance Recording • Loss of generation, loss of load, or loss of major transmission lines may lead to a power system disturbance, possibly affecting customers and power system operations.

Disturbance Recording Applications of PMU in power System Disturbance Recording These figures are examples of long-term data used to analyze the effects of power system disturbances on critical transmission system buses.

7-Transmission and Generation Modeling Verification Applications of PMU in power System 7-Transmission and Generation Modeling Verification • Computerized power system modeling and studies are now the normal and accepted ways of ensuring that power system parameters have been reviewed before large capital expenditures on major system changes. • In years past, actual verification of computer models via field tests would have been either impractical or even impossible • The PMU class of monitoring equipment can now provide the field verification required

7-Transmission and Generation Modeling Verification Applications of PMU in power System 7-Transmission and Generation Modeling Verification • The shown figure compares a remote substation 500 kV bus voltage captured by the PMU to the stability program results

8-Wide – Area protection Applications of PMU in power System 8-Wide – Area protection The introduction of the Phasor Measurement Unit (PMU) has greatly improved the observability of the power system dynamics. Based on PMUs, different kinds of wide area protection, emergency control and optimization systems can be designed

Applications of PMU in power System 9-Fault Location A fault location algorithm based on synchronized sampling. A time domain model of a transmission line is used as a basis for the algorithm development. Samples of voltages and currents at the ends of a transmission line are taken simultaneously (synchronized) and used to calculate fault location.

Modal Transform of synchronized samples Applications of PMU in power System Fault Location The Phasor measurement units are installed at both ends of the transmission line. The three phase voltages and three phase currents are measured by PMUs located at both ends of line simultaneously PMU A Synchronized phasor Modal Transform of synchronized samples PMU B

SPM-based applications in power systems off-line studies real-time monitoring and visualization real-time control, protection and emergency control

CONCLUSIONS The conclusions extracted form the present work can be summarized as follows: A technique for estimating the fault location based on synchronized data for an interconnected network is developed and implemented using a modal transform One-bus deployment strategy is more useful than tree search for fault location detection as it gives more system observability

Conclusions 3- The average value of mode 1 and 2 of Karrenbauer transformation is used for 3-phase and line-to-line faults, while the average value of the 3 modes is used for line-to-line-ground and line-to-ground faults 4- The results obtained from applying the developed technique applied to a system depicted from the Egyptian network show acceptable accuracy in detecting the fault and locations of different faults types.

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